It is known in the art to prepare polymer compositions comprising a thermoplastic polymer matrix within which reinforcing fillers are dispersed. Often these fillers are of organic origin, such as cellulosic or lignocellulosic fibers. Other reinforcing fillers include fiberglass, carbon fibers, graphite fibers, metal fibers, whiskers, aramides, talc, mica, calcium carbonate, glass microspheres, ceramic microspheres, glass wool, rock wool, stainless steel wool, steel wool and gypsum. Certain ceramic fibers are also used as reinforcing fillers, such as alumna, alumna silica and silica. Incorporation of these fillers can impart improved properties, such as stiffness and scratch/mar resistance, to the thermoplastic matrix. For instance, talc is a common polypropylene filler used to increase flexural rigidity and thermal resistance. See U.S. Pat. No. 5,591,795.
Industrial and automotive applications frequently use filled polymer systems to provide desirable mechanical properties, such as stiffness or scratch/mar resistance. However, use of polymer fillers sometimes adversely affect the polymer's surface smoothness and cause deleterious effects on the appearance of scratches or mars in the polymer systems. An example is the white color of a surface scratch often exhibited by a talc-filled polymer system. Many attempts have been made to limit the deleterious effects of the fillers with limited success. See U.S. Patent Publication No. 2005/0,154,101. Therefore, a need exists for polymer compositions exhibiting superior scratch and mar resistance while maintaining the good mechanical properties of the thermoplastic matrix material.
Fillers are known to often be incompatible with the thermoplastic matrix in which one attempts to disperse them. Fillers, in particular fibrous fillers, such as silica fibers, are often surface treated with a silane, usually an organosilane, compound in order to make them more compatible with the thermoplastic matrix. While not wishing to be bound by theory, it is believed that when the silicate is contacted with an organosilane, the silane end bonds to the surface of the silicate. The organic end of the silane compound acts as a wetting agent, making it easier for the thermoplastic to contact and coat the silica surface. Additionally, functionalized (or modified) polyolefins, such as maleated polypropylene or maleated ethylene alpha-olefin copolymers, are used to further compatiblize the filler with the thermoplastic matrix. Suitable functionalized polyolefins are described in U.S. Patent Application Publication No. US 2006/0,009,554, incorporated by reference as if fully disclosed herein. When used, the modified polyolefins form a bridge of sorts between the silane treated silica and the thermoplastic matrix. The silane group binds the silica to the anhydride groups of maleated polypropylene via amide linkages, and the polypropylene backbone becomes entangled with the thermoplastic matrix.
Silane-treatment of fillers is, however, costly, and use of the modified polyolefins further adds to the cost of preparation of the polymer system (and consequently any articles made therefrom). The present invention solves this and other problems by use of untreated fibrous inosilicates as fillers in the inventive polymer compositions.
It is also known in the art to prepare polymer compositions comprising a thermoplastic polymer matrix and a plastomer additive. The plastomer often imparts impact resistance and flexibility to the thermoplastic polymer matrix, thereby rendering it more useful in common applications such as automobile parts. See U.S. Pat. No. 5,747,592, incorporated by reference as if fully disclosed herein.
The present invention provides scratch and mar resistant polymer compositions by combining, in one aspect, a thermoplastic, an ethylene alpha-olefin plastomer, an untreated fibrous inosilicate and a slip agent. In another aspect, a modified olefin polymer is also added to the composition to make the inosilicate more compatible with the thermoplastic matrix. In other aspects, the present invention provides methods for improving the scratch and mar resistance of a thermoplastic material, useful articles formed from the inventive polymer compositions and methods of making the useful articles.